For those who plan to donate, Vitalant recommends eating a healthy, low fat meal within two hours ahead of a donation. The day before, eat a salty snack. When a person donates blood, he or she loses about a gram of salt. Replacing it ahead of time helps keep a person’s blood pressure normal. It’s also recommended that people hydrate by drinking 8 to 16 ounces of non-caffeinated, non-alcoholic beverages one hour before donating. Water is a great choice.